Optical print head, image forming apparatus and light amount correction method of optical print head

ABSTRACT

An optical print head comprises a first light emitting element row, a second light emitting element row, a lens array, a first drive circuit and a second drive circuit. The first light emitting element row includes the arrangement of first light emitting elements. The second light emitting element row includes second light emitting elements arranged in parallel with the first light emitting element row. The lens array concentrates light emitted by the first light emitting elements and the second light emitting elements. The first drive circuit drives each first light emitting element with an identical first current value. The second drive circuit drives each second light emitting element with an identical second current value different from the first current value.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation-in-Part of application Ser. No.15/171,028 filed Jun. 2, 2016, the entire contents of all of which areincorporated herein by reference.

FIELD

Embodiments described herein relate generally to a technology forsuppressing dispersion of light from an optical print head.

BACKGROUND

Conventionally, there is an optical print head in which two rows oflight emitting elements are arranged in parallel below a rod lens arrayin which two rows of rod lenses arranged in parallel are integrated. Thetwo rows of the light emitting elements are positioned alternately in anextending direction of the light emitting element rows.

In the optical print head, there is a case in which undesirabledispersion of light of each light emitted through the rod lens array byeach light emitting element occurs. As the main reason of thedispersion, there is dispersion of luminous efficiency of each lightemitting element and dispersion of a drive circuit connected with eachlight emitting element. As the main reason of the dispersion, there isdispersion of the refractive index distribution of the rod lens arrayand dispersion of a positional relation of each light emitting elementwith respect to each of the rod lens.

In a case of incorporating the optical print head in an image formingapparatus, the light emitted by each light emitting element forms a beamspot corresponding to one dot on a photoconductor. If there isdispersion of light of each light emitting element, density unevennessof an image occurs and the image quality is degraded. Thus, at the timeof shipping the optical print head or at the time of shipping the imageforming apparatus incorporated with the optical print head, a lightamount correction operation for reducing the dispersion of the light isexecuted in manufacturing lines.

The amount of light dispersed by the light emitting element depends onan applied current value and light emitting time. In light amountcorrection, first, currents with the same value are applied to eachlight emitting element, and the light amount of each light emittingelement (light amount of each light emitted through the rod lens arrayby each light emitting element) is measured. Next, under the conditionof the application of the currents with the same value, the lightemitting time of each light emitting element is adjusted with a PWM(Pulse Width Modulation) control so that the amounts of the light of thelight emitting elements become identical. Correction information servingas an adjustment amount of the light emitting time of each lightemitting element is information unique to the optical print head.

In the light amount correction, next, the correction information iswritten into a built-in memory of the optical print head. Throughreading the correction information from the optical print head, thedispersion of the light of each light emitting element can besuppressed.

Incidentally, if the incorporation position of the light emittingelement rows and the rod lens array deviates from an ideal position, adifference occurs in light transmittance. Thus, there is a case in whichthe amounts of light from the light emitting element rows are greatlydifferent. If the amounts of light from the light emitting element rowsare greatly different, there is a problem that the dispersion of thelight cannot be completely suppressed through the light amountcorrection according to the light emitting time.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating control components of an imageforming apparatus;

FIG. 2 is a diagram illustrating the structure of a printer section;

FIG. 3 is a perspective view illustrating the structure of an opticalprint head;

FIG. 4 is a diagram illustrating a positional relation between lightemitting element rows and rod lenses;

FIG. 5 is a diagram illustrating beam spots formed by light emittingelements on photoconductive drums;

FIG. 6 is a cross-sectional diagram illustrating the optical print head;

FIG. 7 is a block diagram illustrating components of an external device;

FIG. 8 is a flowchart illustrating a light amount correction method; and

FIG. 9 is a diagram illustrating a measurement result of amounts oflight of light emitting elements.

DETAILED DESCRIPTION

Generally, in accordance with an embodiment, an optical print headcomprises a first light emitting element row, a second light emittingelement row, a lens array, a first drive circuit and a second drivecircuit. The first light emitting element row refers to the arrangementof first light emitting elements. The second light emitting element rowrefers to the arrangement of second light emitting elements in parallelwith the first light emitting element row. The lens array concentrateslight emitted by the first light emitting elements and the second lightemitting elements. The first drive circuit drives each first lightemitting element with an identical first current value. The second drivecircuit drives each second light emitting element with an identicalsecond current value different from the first current value.

Generally, in accordance with the present embodiment, an image formingapparatus comprises a photoconductor, an optical print head and adeveloping device. The optical print head refers to the foregoingoptical print head which forms an electrostatic latent image on thephotoconductor. The developing device develops the electrostatic latentimage to form a toner image on the photoconductor.

Generally, in accordance with the present embodiment, a light amountcorrection method is a light amount correction method of an opticalprint head which comprises a first light emitting element row includingthe arrangement of first light emitting elements, a second lightemitting element row including the arrangement of second light emittingelements in parallel with the first light emitting element row, and alens array for concentrating light emitted by the first light emittingelements and the second light emitting elements. The light amountcorrection method can include a first step, a second step and a thirdstep. The first step refers to driving the first light emitting elementwith a first current value at a first light emitting time and measuringa first light amount of the first light emitting element through thelens array. The second step refers to driving the second light emittingelement with the first current value at the first light emitting timeand measuring a second light amount of the second light emitting elementthrough the lens array. The third step refers to driving the first lightemitting element with a second current value different from the firstcurrent value at the first light emitting time and measuring a thirdlight amount of the first light emitting element through the lens arrayto calculate a third current value of current through which the lightamount of the first light emitting element through the lens arraybecomes the second light amount when the first light emitting element isdriven at the first light emitting time, or driving the second lightemitting element with a fourth current value different from the firstcurrent value at the first light emitting time and measuring a fourthlight amount of the second light emitting element through the lens arrayto calculate a fifth current value of current through which the lightamount of the second light emitting element through the lens arraybecomes the first light amount when the second light emitting element isdriven at the first light emitting time.

Hereinafter, embodiments are described with reference to theaccompanying drawings.

FIG. 1 is a block diagram illustrating control components of an imageforming apparatus 1.

In the image forming apparatus 1, a processor 94, which is a CPU(Central Processing Unit), executes programs stored in a memory 95 toexecute various processing of the image forming apparatus 1. A display92 displays setting information or operation status of the image formingapparatus 1, log information and notification to a user. An inputsection 93 including a touch panel or buttons receives input of theuser. The processor 94 first reads an image of a document with a scanner91 in a copy processing.

FIG. 2 is a diagram illustrating the structure of a printer section 2.

The processor 94 forms electrostatic latent images based on image dataon photoconductive drums 21Y˜21K with an optical print head 3. The21Y˜21K refers to 21Y, 21M, 21C and 21K. Y is yellow, M is magenta, C iscyan, and K is black. The other reference signs are the same asdescribed above.

The processor 94 develops the electrostatic latent images on thephotoconductive drums 21Y˜21K with developing devices 22Y-22K throughY˜K toners. Y˜K toner images are formed on the photoconductive drums21Y˜21K.

The processor 94 transfers Y˜K toner images on the photoconductive drums21Y˜21K onto a transfer belt 23 in the order of Y, M, C and K in anoverlapped manner. One color image is formed on the transfer belt 23.The processor 94 transfers the color image from the transfer belt 23 toa sheet at a secondary transfer position U. The secondary transferposition U is a position at which a secondary transfer roller 24 and thetransfer belt 23 together form a nip.

The processor 94 heats the sheet with a fixing device 25 and dischargesthe sheet to a tray (not shown) after the image is fixed on the sheet.

FIG. 3 is a perspective view illustrating the structure of the opticalprint head 3.

The optical print head 3 is equipped with a first light emitting elementrow 41, a second light emitting element row 42, a first drive circuit51, a second drive circuit 52, a memory 53 (refer to FIG. 7) and amicrolens array 6.

The light emitting element rows 41 and 42 and the drive circuits 51 and52 are arranged on a substrate 7 made from glass or resin.

A first light emitting element 411 emits light upwards in FIG. 3(direction orthogonal to the substrate 7). The first light emittingelements 411 are arranged in a horizontal scanning direction to form thefirst light emitting element row 41. The horizontal scanning directionrefers to a direction in which a beam spot moves along an axialdirection of the photoconductive drums 21Y˜21K when the first lightemitting element row 41 emits light to the photoconductive drums21Y˜21K.

A second light emitting element 421 emits the light towards the upsideof FIG. 3.

The substrate 7 is a top emission type substrate on which the light isemitted from upper surfaces of the first light emitting element row 41and the second light emitting element row 42 simultaneously.

The second light emitting elements 421 are arranged in a row in thehorizontal scanning direction to form the second light emitting elementrow 42. The second light emitting element row 42 is positioned at oneside (right side in FIG. 3) of the vertical scanning direction withrespect to the first light emitting element row 41. The verticalscanning direction refers to a direction orthogonal to the horizontalscanning direction. The second light emitting element row 42 is arrangedin parallel with the first light emitting element row 41 in the verticalscanning direction.

The light emitting elements 411 and 421 are positioned alternately inthe horizontal scanning direction.

The light emitting elements 411 and 421 can be organicelectroluminescence elements. The light emitting elements 411 and 421each at least include an anode which injects an electron hole, a lightemitting layer having a light emitting area, and a cathode which injectsan electron.

The first drive circuit 51 drives the first light emitting element row41. The first drive circuit 51 can set a current value for the firstlight emitting element row 41. The first drive circuit 51 can executethe PWM control on the first light emitting element 411 individuallythrough the set current value. The first drive circuit 51 canindividually control the light emitting time of the first light emittingelement 411. The first drive circuit 51 is positioned at the one side(left side in FIG. 3) of the vertical scanning direction with respect tothe first light emitting element row 41. The first drive circuit 51 ispositioned at a location nearest to the first light emitting element 411at the end of one side (front side in FIG. 3) of the horizontal scanningdirection among the first light emitting elements 411.

The second drive circuit 52 drives the second light emitting element row42. The second drive circuit 52 can set a current value for the secondlight emitting element row 42. The second drive circuit 52 can executethe PWM control on the second light emitting element 421 individuallythrough the set current value. The second drive circuit 52 can controlthe light emitting time of the second light emitting element 421individually. The second drive circuit 52 is positioned at the otherside (right side in FIG. 3) of the vertical scanning direction withrespect to the second light emitting element row 42. The second drivecircuit is positioned at a location nearest to the second light emittingelement 421 at the end of one side (front side in FIG. 3) of thehorizontal scanning direction among the second light emitting elements421.

The drive circuits 51 and 52 are opposite to each other in the verticalscanning direction.

The first drive circuit 51 is positioned at the one side (left side inFIG. 3) of the vertical scanning direction with respect to the firstlight emitting element row 41. The second drive circuit 52 is positionedat the other side (right side in FIG. 3) of the vertical scanningdirection with respect to the second light emitting element row 42.Thus, the wiring for connecting the first drive circuit 51 with thefirst light emitting element 411 and the wiring for connecting thesecond drive circuit 52 with the second light emitting element 421 arenot overlapped.

The rod lens array 6 is equipped with a plurality of integrated columnarrod lenses 611 and 621. The rod lenses 611 are arranged in a row in ascanning direction to form a rod lens row 61. The rod lenses 621 arearranged in a row in the scanning direction to form a rod lens row 62.The rod lens rows 61 and 62 are arranged in the vertical scanningdirection in parallel. The rod lens array 6 is positioned at the upperside in FIG. 3 of the light emitting element rows 41 and 42 and oppositeto the light emitting element rows 41 and 42. The rod lens array 6enables the light emitted by each of the light emitting elements 411 and421 to be imaged on the photoconductive drums 21Y˜21K as beam spots.

In the present embodiment, the rod lens rows 61 and 62 are arrangedcorresponding to the first and the second light emitting element rows 41and 42. However, one rod lens row may be arranged corresponding to aplurality of (e.g., 2) light emitting element rows.

FIG. 4 is a diagram illustrating a positional relation between the lightemitting element rows 41 and 42 and the rod lenses 611 and 621.

The diameter of each of the rod lenses 611 and 621 is, for example, 900μm.

The light emitting surface of each of the light emitting elements 411and 421 is a rectangular shape and dimension of two sides (length andwidth) of the light emitting surface is 30 μm*30 μm, for example.

The light emitting elements 411 and 421 are arranged alternately in thehorizontal scanning direction (right and left direction of FIG. 4). Ifresolution in the horizontal scanning direction is 1200 dpi, forexample, the interval of the central parts of the light emittingelements 411 and 421 adjacent to each other in the horizontal scanningdirection is 21 μm (=25.4 mm/1200). The number of the light emittingelements 411 and 421 is 15360 in total. The interval of the centralparts of the light emitting elements 411 and 421 in the verticalscanning direction (up and down direction of FIG. 4) is 105 μm.

Light emitted by the first light emitting element 411 largely passesthrough the rod lens 611 or 621 positioned directly above such a firstlight emitting element 411. Since the light emitted by the first lightemitting element 411 is diverging light, the light also passes throughother rod lenses 611 and 621. The light emitted by the first lightemitting element 411 is concentrated on a single spot on thephotoconductive drums 21Y˜21K by the plurality of rod lenses 611 and621. Similarly, light emitted by the second light emitting element 421is concentrated on a single spot on the photoconductive drums 21Y˜21K bythe plurality of rod lenses 611 and 621.

As shown in FIG. 5, on the photoconductive drums 21Y˜21K, beam spots411A formed by the respective first light emitting elements 411 arearranged in a row in the horizontal scanning direction. The interval ofthe beam spots 411A is the same as the interval of the first lightemitting elements 411. Similarly, beam spots 421A formed by the secondlight emitting elements 421 are arranged in a row in the horizontalscanning direction. The interval of the beam spots 421A is the same asthe interval of the second light emitting elements 421.

In the image forming apparatus 1 of the present embodiment, after one ofthe light emitting elements, 411 (or 421), are lighted while rotatingthe photoconductive drums 21Y˜21K, the other one of the light emittingelements, 421 (or 411), can be lighted. Thus, the beam spots 421A eachformed by the other light emitting element 421 can be positioned betweenthe beam spots 411A each formed by the one light emitting element 411 asshown in FIG. 5. In other words, the beam spots 411A and 421A formed bythe light emitting elements 411 and 421 can be arranged in a row in thehorizontal scanning direction.

In the present embodiment, the light emitting element rows 41 and 42 areprovided in two rows in the vertical scanning direction. Thus, bydriving the light emitting elements 411 and 421 as described above, theresolution in the scanning direction can become twice as compared to acase in which there is one light emitting element row.

In the present embodiment, the light emitting elements 411 and 421 arearranged in two rows. Thus, the first light emitting elements 411 can beprevented from interfering with the second light emitting elements 421even when the areas of the light emitting elements 411 and 421 areincreased. Thus, in the present embodiment, the areas of the lightemitting elements 411 and 421 can be increased without changing thepositional relation of the central parts between the first lightemitting elements 411 and between the second light emitting elements421, i.e., without changing the resolution.

FIG. 6 is a cross-sectional diagram illustrating the optical print head3.

A lid 82 blocks the internal space of a holder 81. The lid 82 holds thesubstrate 7. The light emitting elements 411 and 421 on the substrate 7are sealed by a sealing glass 83. The holder 81 positions the rod lensarray 6 and positions the substrate 7 at an operating distance of therod lens array 6.

FIG. 7 is a block diagram illustrating components of an external device100.

In the manufacturing line of the image forming apparatus 1, the externaldevice 100 is connected with the optical print head 3. The externaldevice 100 is equipped with a processor 101, a memory 102, a lightreceiving device 103, a display 104 and an input device 105. Theprocessor 101 acting as a CPU executes programs stored in the memory 102to execute various processing of the external device 100. Light emittedby the light emitting elements 411 and 421 through the rod lens array 6is concentrated on a light receiving surface of the light receivingdevice 103. The light receiving device 103 is configured so that thelight amounts of the beam spots formed by the light emitting elements411 and 421 on the light receiving surface of the light receiving device103 are equal to the light amounts of the beam spots 411A and 421A onthe photoconductive drums 21Y˜21K. The light receiving device 103 mayexamine the light emitting element rows 41 and 42 by one row at a time.Alternatively, the light receiving device 103 may be configured toexamine the two rows of the light emitting elements 411 and 421simultaneously. The display 104 displays setting information oroperation status of the external device 100, log information andnotification to the user. The input device 105 including a touch panelor buttons receives input of the user.

The external device 100 executes the following light amount correctionprocessing for suppressing dispersion of light emitted by the lightemitting elements 411 and 421 through the rod lens array 6.

FIG. 8 is a flowchart illustrating the light amount correction method.FIG. 9 shows a measurement result obtained by the external device 100when the light emitting elements 411 and 421 are driven with a firstcurrent value α1 at a first light emitting time T1. The measurementresult shows a measurement result of light amounts L1 and L2 of thelight emitting elements 411 and 421 through the rod lenses 611 and 621.

The external device 100 drives the light emitting elements 411 and 421with the first current value α1 at the first light emitting time T1simultaneously with the drive circuits 51 and 52 (ACT 1).

The external device 100 measures the first light amount L1 of each firstlight emitting element 411 through the rod lenses 611 and 621, and thesecond light amount L2 of each second light emitting element 421 throughthe rod lenses 611 and 621 (ACT 2).

Here, with reference to FIG. 4, as the light emitted by each of thelight emitting elements 411 and 421 passes through a position closer tothe central part of each of the rod lenses 611 and 621, the lightconcentrating function by the rod lenses 611 and 621 is moreintensified. Consequently, the light amount on the beam spot formed bysuch light on the photoconductive drums 21Y˜21K is increased. Thus, asindicated by a chain line in FIG. 4, ideal positions of the lightemitting element rows 41 and 42 are located in a region between the rodlenses 611 and 621 in which distances from the central parts of the rodlenses 611 and 621 to the first light emitting element row 41 are thesame as distances from the central parts of the rod lenses 611 and 621to the second light emitting element row 42.

However, the light emitting elements 411 and 421 is very small ascompared to the diameter of each of the rod lenses 611 and 621, and theinterval between the light emitting element rows 41 and 42 is also verysmall. Thus, if the incorporation position of each component is deviatedfrom the ideal position, a case in which the positions of the lightemitting element rows 41 and 42 are both biased towards one of the rodlens rows 61 and 62 occurs. In the present embodiment, the positions ofthe light emitting element rows 41 and 42 are both biased towards therod lens row 62.

Moreover, in the present embodiment, the second light emitting elementrow 42 passes through a position closer to the central part of the rodlens 621 than the first light emitting element row 41.

In the present embodiment, the second light emitting element row 42passes through a position closer to the central part of the rod lensarray 62 than the first light emitting element row 41. Thus, the lightconcentrating function of the rod lens 621 is exerted more strongly onthe second light emitting element row 42 than on the first lightemitting element row 41. The light concentrating function of the rodlens 611, on the other hand, is exerted more strongly on the first lightemitting element row 41 than on the second light emitting element row42. However, since the rod lens 611 is farther away from the lightemitting element rows 41 and 42 than the rod lens 621, the function ofthe rod lens 611 is weaker than that of the rod lens 621.

Consequently, as shown in FIG. 9, the light amount of the second lightemitting element 421 of the second light emitting element row 42 onwhich the light concentrating function of the rod lens 621 is stronglyexerted is 10% on an average more than that of the first light emittingelement 411 of the first light emitting element row 41. Thus, when thedispersion of the light in the light emitting element rows 41 and 42 islarge as described above, the dispersion of the light of each of thelight emitting elements 411 and 421 cannot be sufficiently suppressedthrough the conventional light amount correction according to the lightemitting time, which causes image degradation.

After ACT 2, the external device 100 drives the second light emittingelement row 42 having a larger light amount between the light emittingelement rows 41 and 42 with a second current value α2 smaller than thefirst current value α1 at the first light emitting time T1 (ACT 3). Thesecond current value α2 is set to a value so that a third light amountL3 of the second light emitting element 421 at the time of applying acurrent with the second current value α2 is smaller than the first lightamount L1 of the first light emitting element 411 corresponding to thesecond light emitting element 421. Hereinafter, the first light emittingelement 411 corresponding to the second light emitting element 421refers to the first light emitting element 411 corresponding to thesecond light emitting element 421 in the vertical scanning direction.Further, the first light emitting element 411 corresponding to thesecond light emitting element 421 refers to the first light emittingelement 411 having the same number as the second light emitting element421 when the light emitting elements 411 and 421 are each numbered fromone side of the scanning direction.

The external device 100 measures the third light amount L3 of eachsecond light emitting element 421 of the second light emitting elementrow 42 (ACT 4).

The relation between the current value and the light amount is aproportional relation. For example, in FIG. 9, the difference (L2-L3) ofthe amounts of light of a certain second light emitting element 421 atthe time of being driven with the first and the second current values α1and α2 different from each other is obtained by multiplying aproportionality coefficient K by the difference (α1−α2) of the currentvalues and is indicated by the following formula (1).

L2−L3=K(α1−α2)  (1)

The external device 100 calculates the proportionality coefficient Kbased on the formula (1) (ACT 5).

The external device 100 calculates a third current value α3 of a certainsecond light emitting element 421 based on the following formula (2)when the light amount at the time of driving the second light emittingelement 421 at the first light emitting time T1 is equal to the firstlight amount L1 at the time of driving the first light emitting element411 corresponding to the second light emitting element 421 with thefirst current value α1 at the first light emitting time T1 (ACT 6).

L2−L1=K(α1−α3)  (2)

By driving each of the second light emitting elements 421 with the thirdcurrent value α3, alight amount L3 of each second light emitting element421 (e.g., LEDs No. 1˜50 in FIG. 9) becomes substantially the same asthe light amount L1 of each of the first light emitting elements 411(e.g., LEDs No. 1˜50 in FIG. 9) corresponding to each second lightemitting element 421 and driven with the first current value α1.

As described above, in this correction processing, the levels of thelight amounts of the light emitting element rows 41 and 42 are firstequalized by correcting the current values of the light emitting elementrows 41 and 42. Thereafter, the light emitting time of each of the lightemitting elements 411 and 412 is corrected by the following processingACT 7 to suppress the dispersion of the light of each of the lightemitting elements 411 and 412.

The external device 100 calculates a second light emitting time T2 atwhich a target light amount (reference light amount) is obtained foreach first light emitting element 411 at the time of executing the PWMcontrol by taking the current value of the first light emitting element411 as the first current value α1.

The external device 100 calculates a third light emitting time T3 atwhich a target light amount is obtained for each second light emittingelement 421 at the time of executing the PWM control by taking thecurrent value of the second light emitting element 421 as the thirdcurrent value α3.

The external device 100 writes the correction information such as thefirst and the third current values α1 and α3 and the second lightemitting time T2 and the third light emitting time T3 into the built-inmemory 53 (FIG. 7) of the optical print head 3 (ACT 7).

If the optical print head 3 is incorporated in the apparatus andreceives an instruction for driving the light emitting elements 411 and421, the first and the second drive circuits 51 and 52 drives the lightemitting elements 411 and 421 according to the correction information.

In this case, the first drive circuit 51 drives each first lightemitting element 411 with the same first driving current value (e.g.,the first current value α1). The first drive circuit 51 drives, based onthe second light emitting time T2 calculated for each of the first lightemitting elements 411, each first light emitting element 411 at thelight emitting time corresponding to each target gradation value,respectively.

The second drive circuit 52 drives each second light emitting element421 with the same second driving current value (e.g., the third currentvalue α3). The second drive circuit 52 drives, based on the third lightemitting time T3 calculated for each of the second light emittingelements 421, each second light emitting element 421 at the lightemitting time corresponding to each target gradation value,respectively.

In the present embodiment, as the drive circuits 51 and 52 are providedfor each of the light emitting element rows 41 and 42, the lightemitting element rows 41 and 42 can be driven with different currentvalues and the dispersion of the light of the light emitting elementrows 41 and 42 can be suppressed.

In the conventional technique, the dispersion of light among the lightemitting elements 411 and 421 is adjusted by adjusting the lightemitting time. When the optical print head 3 includes a plurality oflight emitting element rows 41 and 42, however, the dispersion of lightof the light emitting element rows 41 and 42 may be large as shown inFIG. 9. In this case, the dispersion of the light of the light emittingelement rows 41 and 42 cannot be sufficiently suppressed through theconventional light amount correction according to the light emittingtime, which causes image degradation.

According to the present embodiment, however, the levels of the lightamounts of the light emitting element rows 41 and 42 are equalized bycorrecting the current values of the light emitting element rows 41 and42. After that, the dispersion of the light of each of the lightemitting elements 411 and 421 is corrected with the light emitting timein the present embodiment. Thus, even when the dispersion of the lightof the light emitting element rows 41 and 42 is large, such dispersioncan be sufficiently corrected.

The number of the first drive circuit 51 for driving the first lightemitting element row 41 is not limited to one. The first light emittingelements 411 may be classified into several groups and a plurality ofthe first drive circuits 51 may be set respectively corresponding to thegroups. The second drive circuit 52 is the same as the first drivecircuit 51.

The drive circuits 51 and 52 may be arranged at positions sandwichingthe first and the second light emitting element rows 41 and 42 in thevertical scanning direction.

In the above embodiment, the external device 100 is configured toequalize the light amount of the second light emitting element row 42with the light amount of the first light emitting element row 41 bydecreasing the current value of the second light emitting element row 42having a larger light amount. Alternatively, the light amount of thefirst light emitting element row 41 may be equalized with the lightamount of the second light emitting element row 42 by increasing thecurrent value of the first light emitting element row 41 having asmaller light amount. In the case of decreasing the current value, thelight amounts of the light emitting elements 421 and 411 are more likelyto decrease to the target value even when some of the light emittingelements 421 and 411 have inadequate quality. In the case of increasingthe current value, however, when some of the light emitting elements 421and 411 have inadequate quality, there is a possibility that the lightamounts of such light emitting elements 421 and 411 cannot achieve thetarget value. Thus, in the light amount correction processing, it ismore preferable that the light amount of the second light emittingelement row 42 be equalized with the light amount of the first lightemitting element row 41 by decreasing the current value of the secondlight emitting element row 42 having a larger light amount.

The lens array for concentrating the light emitted by the light emittingelements 411 and 421 may be a lens array other than the rod lens array6.

As described above in detail, according to the technology described inthe specification, a technology for suppressing the dispersion of thelight from the optical print head can be supplied.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the invention. Indeed, the novel novel embodiments describedherein may be embodied in a variety of other forms; furthermore, variousomissions, substitutions and and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinvention. The accompanying claims and their equivalents are intended tocover such forms or modifications as would fall within the scope andspirit of the invention.

What is claimed is:
 1. An optical print head comprising: a first lightemitting element row configured to include arrangement of first lightemitting elements; a second light emitting element row configured toinclude second light emitting elements arranged in parallel with thefirst light emitting element row; a lens array configured to concentratelight emitted by the first light emitting element and the second lightemitting element; a first drive circuit configured to drive each firstlight emitting element with an identical first current value; and asecond drive circuit configured to drive each second light emittingelement with an identical second current value different from the firstcurrent value.
 2. The optical print head according to claim 1, whereinthe first drive circuit is positioned at one side of a second directionorthogonal to a first direction along which the first light emittingelement row extends with respect to the first light emitting elementrow, and the second light emitting element row is positioned at theother side of the second direction with respect to the first lightemitting element row and the second drive circuit is positioned at theother side of the second direction with respect to the second lightemitting element row.
 3. The optical print head according to claim 1,further comprising a memory configured to store a third current valueand a fourth current value when the amounts of light of the first lightemitting element and the second light emitting element through the lensarray are the same at the time of driving the first light emittingelement with the third current value and driving the second lightemitting element with the fourth current value at the same lightemitting time simultaneously, a light emitting time of the first lightemitting element when light amount of each first light emitting elementthrough the lens array reaches a reference light amount at the time ofdriving each first light emitting element with the third current valueand a light emitting time of the second light emitting element whenlight amount of each second light emitting element through the lensarray reaches the reference light amount at the time of driving eachsecond light emitting element with the fourth current value.
 4. Theoptical print head according to claim 2, wherein the first drive circuitis positioned at a location nearest to the first light emitting elementlocated at the end of one side of the first direction among the firstlight emitting elements; and the second drive circuit is positioned at alocation nearest to the second light emitting element located at the endof the one side of the first direction among the second light emittingelement.
 5. The optical print head according to claim 1, wherein thefirst light emitting element and the second light emitting element arepositioned alternately in the first direction.
 6. The optical print headaccording to claim 1, wherein the first light emitting element and thesecond light emitting element are organic electroluminescence elements.7. An image forming apparatus, comprising: a photoconductor; an opticalprint head according to claim 1 configured to expose the photoconductorto form an electrostatic latent image on the photoconductor; and adeveloping device configured to develop the electrostatic latent imageto form a toner image on the photoconductor.
 8. Alight amount correctionmethod of an optical print head, the optical print head comprising afirst light emitting element row configured to include arrangement offirst light emitting elements, a second light emitting element rowconfigured to include second light emitting elements arranged inparallel with the first light emitting element row, and a lens arrayconfigured to concentrate light emitted by the first light emittingelement and the second light emitting element, the method comprising: afirst step of driving the first light emitting element with a firstcurrent value at a first light emitting time and measuring a first lightamount of the first light emitting element through the lens array; asecond step of driving the second light emitting element with the firstcurrent value at the first light emitting time and measuring a secondlight amount of the second light emitting element through the lensarray; and a third step of driving the first light emitting element witha second current value different from the first current value at thefirst light emitting time and measuring a third light amount of thefirst light emitting element through the lens array to calculate a thirdcurrent value of current through which the light amount of the firstlight emitting element through the lens array becomes the second lightamount when the first light emitting element is driven at the firstlight emitting time, or driving the second light emitting element with afourth current value different from the first current value at the firstlight emitting time and measuring a fourth light amount of the secondlight emitting element through the lens array to calculate a fifthcurrent value of current through which the light amount of the secondlight emitting element through the lens array becomes the first lightamount when the second light emitting element is driven at the firstlight emitting time.
 9. The method according to claim 8, whereinperformed in the third step is, if the first light amount is greaterthan the second light amount, calculating the third current value, andif the second light amount is greater than the first light amount,calculating the fifth current value.
 10. The method according to claim8, wherein the optical print head includes a first drive circuit and asecond drive circuit, the first drive circuit is positioned at one sideof a second direction orthogonal to a first direction along which thefirst light emitting element row extends with respect to the first lightemitting element row to drive the first light emitting element row, thesecond light emitting element row is positioned at the other side of thesecond direction with respect to the first light emitting element row,and the second drive circuit is positioned at the other side of thesecond direction with respect to the second light emitting element rowto drive the second light emitting element row.